Along an assembly line, diapers and various types of other disposable absorbent articles may be assembled by adding components to and otherwise modifying advancing, continuous webs of material. Webs of material and component parts used to manufacture diapers may include: backsheets, topsheets, absorbent cores, front and/or back ears, fastener components, and various types of elastic webs and components such as leg elastics, barrier leg cuff elastics, and waist elastics. In some configurations, graphics are printed on individual components and/or continuous webs of material used to assemble the absorbent articles. The graphics may be provided by printing ink on substrate materials by various printing methods, such as flexographic printing, rotogravure printing, screen-printing, inkjet printing, and the like.
In some configurations, the printing operations are performed separate to the assembly process, such as for example, printing the substrates offline wherein the printed substrates may be stored until needed for production. For example, printing operations may be accomplished on discrete printing lines, separately from converting lines that are dedicated to manufacturing disposable absorbent articles. After printing on the printing lines, the printed substrates are delivered to the converting lines, such as in a form of continuous webs comprising printed images thereon. However, the above practice of separately printing the substrates offline from the converting lines typically requires additional cost associated with handling, winding and unwinding, storing and shipping of the substrates. In addition, the above steps can negatively affect the quality of the printed substrate, resulting in uneven and often excessive deformations of the wound layers of the substrate inside the roll due to uneven distribution of the compression forces inside the roll. Furthermore, the separately printed substrates often require special registration control methods to ensure proper phasing of the printed images with the converting operations to effect a desired and consistent positioning of the printed image in the produced article.
In an attempt to overcome the aforementioned drawbacks to offline printing, the graphic printing may be done online during the article assembly process. However, combining printing operations with converting operations may create other challenges in performing such printing processes when attempting to maintain aesthetically pleasing final assemblies. For example, contact printing processes, such as flexographic and rotogravure printing processes, may be capable of operating effectively on certain substrates at relatively high production rates. However, such contact printing processes have relatively low degrees of flexibility with regard to the ability to change the design of a printed graphic. When utilizing such contact printing methods, changes in graphic designs would often necessitate the shutdown and restart of the entire converting operation. In contrast, some types of printing processes, such as non-contact inkjet printing processes, may provide relatively high degrees of flexibility and ease with regard to the ability to change the design of a printed graphic. In some configurations, a change in graphic design can be implemented by simply inputting commands to a programmed printhead controller to select a desired image to be printed.
However, such non-contact printing processes may have limited ability to print graphics having desired contrasts at relatively high speed production rates. Contrasts herein may be represented and/or expressed in terms of delta E* values and/or optical densities. For example, drop-on-demand inkjet printheads may be configured to discharge ink from orifices in the printhead onto an area of a substrate advancing in a machine direction MD beneath the printhead. Each time the printhead “fires,” a drop of ink is discharged from an orifice. The frequency at which the printhead fires affects the print resolution in the machine direction of the printed area on the substrate in dots per inch (dpi). For a given machine direction substrate advancement speed, a higher firing frequency will yield a higher MD print resolution (dpi), and conversely, a lower firing frequency will yield a lower MD print resolution (dpi). Thus, depending on the MD advancement speed of a substrate, a printhead may be programmed to fire at a frequency high enough to achieve a desired MD print resolution. In turn, a relatively higher MD print resolution will result in a printed region with a relatively higher contrast.
When utilizing such printheads in converting lines operating at high production rates, substrates may be required to advance at speeds past the printhead such that printhead would have to fire at a frequency that would exceed the maximum frequency of the printhead in order to achieve the desired MD print resolution, and in turn, the desired contrast. As such, in some scenarios, the converting line would either have to operate at relatively lower production speeds to achieve the desired MD print resolutions, or operate at relatively higher production rates while printing graphics with less than desired MD print resolutions. In other scenarios, it may be possible to equip the converting line with printheads designed fire at the relatively high firing frequencies required to achieve the desired MD print resolutions. However, such high frequency printheads may be cost prohibitive. In yet other scenarios, printheads may be configured to print ink with relatively large drop sizes at relatively low MD print resolutions to achieve the desired contrasts. However, the spacing between adjacent ink droplets may be readily noticeable, and in turn, may detract from aesthetically pleasing aspects of the printed regions.
Consequently, there remains a need to configure converting lines with online non-contact printheads to print areas of substrates at desired contrasts, wherein the converting lines are operable at relatively high productions speeds while printing desired MD print resolutions achievable at or below the maximum firing frequencies of the printheads.